WASHINGTON -- A rising star got the best of a veteran ace in a battle of right-handed starters on Thursday night.
Washington's Jordan Zimmermann improved to 10-3 as he allowed one unearned run in eight innings of the Nationals' 5-1 victory over the Colorado Rockies.
The win spoiled the major league return of Rockies starter Roy Oswalt, who had 11 strikeouts in five innings but gave up nine hits and four earned runs.
"I felt strong. Overall, I felt pretty well," said Oswalt, who threw 101 pitches. "I kind of got my pitch count up. I knew it was getting up because of the strikeouts."
Rockies manager Walt Weiss said, "I felt Roy threw the ball extremely well. He had a really good fastball. I thought he looked great. He is a strong guy. He is more physical than people think."
Zimmermann, who is now 4-0 lifetime against the Rockies, allowed six hits with nine strikeouts and one walk before being lifted for a pinch-hitter in the bottom of the eighth. He lowered his ERA to 2.26.
"He was pretty much in control the whole game," Rockies first baseman Todd Helton said. "We didn't do enough the win the game."
Weiss said of Zimmermann: "It's a big fastball. He throws strikes with everything. He is impressive. He is a power arm."
Zimmermann threw an impressive 85 of 112 pitches for strikes.
"It was successful. How can you say it was too many strikes? That is just his makeup," Nationals pitching coach Steve McCatty said. "He doesn't like to walk people."
It was the fourth loss in a row for the Rockies (37-37). Washington (36-36) is back at .500 after losing four of six ganes before Thursday.
"We need to start playing some consistent ball," said Washington first baseman Adam LaRoche, who contributed three hits said Zimmermann should "absolutely" make the National League All-Star team.
Zimmermann helped his own cause with a sacrifice fly in the sixth to make it 5-0.
Colorado scored in the eighth against Zimmermann on a RBI single by D.J. LeMahieu after rookie second baseman Anthony Rendon made a throwing error on a ground ball off the bat of Tyler Colvin.
LaRoche gave the Nationals a 5-0 lead in the fifth when he hit a two-run triple to right center.
Washington had taken a 2-0 lead in the fourth on a two-out single by Kurt Suzuki that scored LaRoche from second on a close play at the plate.
Ian Desmond had given Washington a 1-0 lead in the second with a one-out homer to left against Oswalt, who was 3-2 with a 2.16 ERA for the Rockies' Double-A Tulsa affiliate before he was promoted to the big leagues. It was the 11th homer of the year for Desmond and the second in as many at-bats. He hit a grand slam in the 11th inning on Wednesday against the Philadelphia Phillies in a 6-2 win.
Oswalt was signed by the Rockies on May 3 and entered the game with a 7-5 career record against the Nationals and an overall major-league record of 163-96 with a 3.28 ERA.
The last big-league appearance for Oswalt was Oct. 2 at Oakland while with the Texas Rangers.
Zimmermann has not lost at Nationals Park since May 2012, going 12-0 during that span.
Washington closer Rafael Soriano pitched a scoreless ninth in a non-save situation.
NOTES: To make room for Oswalt, the Rockies sent LHP Jeff Francis to Triple-A Colorado Springs. "I am glad Jeff is still with us (in the system). He has meant so much to this organization," Weiss said. The Rockies also designated RHP Chris Volstad for assignment. ... Johnson said OF Bryce Harper, on the DL since early June with left knee bursitis, continues to make progress. "He ran in the outfield today. He will hit in the cage today. He is close" to starting a minor-league rehab assignment, Johnson said. ... Colorado RF Michael Cuddyer is a native of Norfolk, Va. and his wife, Claudia, graduated from Washington-Lee High in Arlington, Va., about 10 miles from Nationals Park. Cuddyer rented a suite for the game to mark their son Casey's fifth birthday. Cuddyer expected about 25 family and friends at the game. He singled in the first to extend his career-best hitting streak to 18 games.